JP2518865Y2 - Channel selection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for selecting a channel in a device for receiving a television signal.

<Prior Art> Conventionally, the above-mentioned channel selection device has been used in a tuner for satellite broadcast reception as shown in FIG. 3, for example. In the figure, reference numeral 2 denotes a high frequency amplification / frequency conversion unit, which is a BS-IF signal of 1 GHz band from a converter for receiving satellite broadcasting supplied to an input terminal 4 (this BS-IF signal is FM-modulated as well known. Since it is a frequency-converted satellite broadcast signal, it is, of course, FM-modulated.) And the oscillation of the built-in local oscillation circuit according to the frequency control signal from the frequency adjustment unit 6 is amplified. By controlling the frequency, BS-IF of a predetermined channel is selected from the amplified BS-IF signal.
Extract the IF signal, convert it to a second intermediate frequency signal,
It is supplied to the IF processing unit 8. The frequency adjusting unit 6 generates a frequency control signal in accordance with a channel selection signal from the channel selecting unit 10 that indicates which channel to select and an AFC input signal from the IF processing unit 8. The frequency adjusting unit 6 and the channel selecting unit 10 constitute a channel selecting device.

The second intermediate frequency signal processed by the IF processing unit 8 is FM-detected by the detection amplification unit 12, and the video signal separated from the detected signal is amplified and then amplified via the variable resistor 14 to the video amplification unit. It is supplied to 16 and is amplified here and supplied to the video output terminal 18. On the other hand, the audio signal separated from the detected signal is demodulated by the audio demodulation unit 20, amplified by the audio amplification unit 22, and then supplied to the audio output terminal 24.

<Problems to be solved by the invention> In the tuner for receiving satellite broadcasting shown in FIG. 3, a variable resistor is used.
14 is for adjusting the video level, but 1
Since the video levels of a plurality of satellite television signals transmitted from one broadcasting satellite are the same, once the variable resistor 14 is operated to adjust the video level, it is not necessary to adjust the channel thereafter. . However,
When multiple satellite television signals are transmitted from multiple broadcasting satellites, such as European satellite broadcasting,
The video level is different for each broadcasting satellite, and the variable resistor 14 is operated each time the channel is switched from the state where the television signal from a certain broadcasting satellite is received to the state where the television signal of another broadcasting satellite is received. Then, unless the video level is adjusted again, a good reception screen cannot be obtained, and this adjustment must be performed frequently, which is a troublesome problem.

<Means for Solving Problems> In order to solve the above problems, the present invention proposes a method for detecting the intermediate frequency signal from the frequency conversion unit by FM detection at a stage subsequent to the detection unit. In a video signal processing device provided with an attenuator capable of changing the amount of attenuation, the channel selector is provided with an attenuation controller that generates the above-mentioned attenuation control signal. Accordingly, the magnitude of the attenuation control signal is changed so that the attenuation amount is suitable for the selected channel.

<Operation> It is known from which broadcasting satellite the satellite broadcasting television signal of which channel is transmitted, and the necessary attenuation amount is known according to the video level of each channel. The magnitude of the damping control signal required is also known. Therefore, if the attenuation control unit is adjusted so as to generate the required attenuation control signal and the attenuation control signal having a magnitude corresponding to the channel selection signal is supplied to the attenuation unit, the attenuation control signal is changed each time the channel is switched. The video level can be automatically adjusted to a size suitable for the channel.

<Effect> As described above, according to the present invention, the baseband video signal obtained by performing FM detection of the FM-modulated intermediate frequency signal by the detection unit is attenuated by the attenuation unit, and the attenuation amount is The attenuation control section supplies an attenuation control signal having a magnitude corresponding to the channel selection signal to the attenuating section so as to correspond to the channel of the detected baseband video signal. Therefore, no matter which channel is switched, the baseband video signal can be automatically adjusted to a level suitable for the switched channel, and it is necessary to adjust the level of the baseband video signal each time the channel is switched. There is no. Moreover, according to this invention, it is not necessary to determine the type of the received baseband video signal by using a decoder or the like, and the channel selection device always uses the channel selection signal that is always used. Can be simplified.

<Embodiment> FIGS. 1 and 2 show an embodiment in which the channel selection device according to the present invention is applied to a satellite broadcast receiving tuner. The same parts as those of the conventional tuner for receiving satellite broadcast shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, an attenuation unit 26 is provided between the detection amplification unit 12 and the video amplification unit 16. The attenuator 26 is a combination of two transistor switch circuits and a resistance attenuator circuit (not shown), which can switch on / off of the transistor to the level of the applied attenuation control voltage, thereby varying the attenuation amount. It is a publicly known thing that can.

The attenuation control voltage to the attenuator 26 is given by the attenuation controller 28. The attenuation control unit 28, the frequency adjusting unit 6, and the channel selecting unit 10 constitute a channel selecting device.

Details of the attenuation controller 28 and the frequency adjuster 6 are shown in FIG. First, the frequency adjusting unit 6 will be described. In this embodiment, any of the eight channels can be selected, and terminals 30a to 30h are provided corresponding to the eight channels, respectively. These terminals 30a to 30h are
It is configured to be at L level when selected by the channel selection unit 10. A series circuit of fixed resistors 32a to 32h and diodes 34a to 34h is connected to each of the terminals 30a to 30h, and these diodes 34a to 34h are connected to the input side of the buffer amplifier 36.
On the other hand, the connection points of the fixed resistors 32a to 32h and the diodes 34a to 34h are fixed resistors 39a to 39h on the arms of the variable resistors 38a to 38h provided so as to correspond to the terminals 30a to 30, respectively. It is connected. Each of these variable resistors 38a
One end of each of 38 to 38h is connected to the output side of the amplifier 42 that amplifies the AFC error input from the IF processing unit 8 and the power supply unit via the diode 40.

When no channel is connected, each terminal
30a to 30h are H level, and each diode 34a to 34h
Are non-conductive, and the frequency control voltage is not applied to the buffer amplifier 36. For example, when the terminal 30a becomes L level, the diode 34a becomes conductive and the amplifier 4
The superimposed voltage of the amplified voltage of the AFC error input from 2 and the power supply voltage is divided by the variable resistor 38a and the fixed resistors 39a and 32a, which is supplied to the buffer amplifier 36 as the frequency control voltage, which is amplified. And is supplied to the VCO 43 which is a local oscillation circuit in the high frequency amplification frequency conversion unit 2. Therefore, by appropriately adjusting the position of the arm of the variable resistor 38a, it is possible to receive the satellite broadcast television signal of a predetermined channel. Other channels also have variable resistors 38b through 38h
If you adjust the position of the arm of the
It can be received when 30b to 30h become L level. In addition,
44 is a variable resistor for AFC fine adjustment.

Next, the attenuation control unit 28 has three contact changeover switches 46a to 46h corresponding to the terminals 30a to 30h, respectively. For the L contacts of these three-contact changeover switches 46a to 46h,
A voltage of 11.5V is applied, a voltage of 6V is applied to the M contact, and a voltage of 0V is applied to the H contact. When the common terminal is switched to the H contact of each changeover switch 46a to 46h, a large amount of attenuation is obtained, and when the common terminal is switched to the M contact, an intermediate amount of attenuation is obtained,
When the common terminal is switched to the L contact, the minimum attenuation amount is obtained. In each of the changeover switches 46a to 46h, which of the H, M, and L contacts is to be used to switch the common terminal is to actually receive each channel and switch the common terminal so as to obtain the best reception state. decide. The common terminal of the changeover switch 46a is connected to the bases of the transistors 50 and 51 via the electronic switch 48a in the IC1, and the common terminal of the changeover switch 46b is the base of the transistors 50 and 51 via the electronic switch 48b in the IC1. The common terminal of the changeover switch 46c and the common terminal of the changeover switch 46d are similarly connected to the bases of the transistors 50 and 51 via the electronic switches 48c and 48d in the IC1. Similarly, changeover switches 46e-46h
The common terminal of is also connected to the bases of the transistors 50 and 51 via the electronic switches 48e to 48h in the IC2. Each of the electronic switches 48a to 48h is configured to be closed when the control terminals 50a to 50h are set to the H level. These control terminals 50a to 50h are respectively connected to the terminals 30a to 30h via the inverters 52a to 52h formed by the 2-input NAND circuits in the ICs 3 and 4, respectively.

Therefore, when the terminal 30a becomes L level, the output of the inverter 52a becomes H level at the same time, and the electronic switch 48a
Is closed. As a result, the common terminal of the changeover switch 46a is in contact with the H contact to which 0V is applied,
0V is applied to the transistor 5 via the closed electronic switch 48a.
Applied to the base of 0,51. As a result, transistor 5
0 and 51 become non-conducting state, + 12V of transistors 50 and 51
Is applied to the attenuator 26, and the attenuator 26 has a large amount of attenuation. Therefore, the video level of the satellite broadcast signal of the selected channel is greatly attenuated by the terminal 30a becoming the L level.

When the terminal 30b becomes L level, the output of the inverter 52b becomes H level and the electronic switch 48b is closed. As a result, the common terminal of the changeover switch 46b is 11.5V.
11.5V is applied to the transistors 50 and 51 via the closed electronic switch 48b.
Applied to the base of. As a result, the transistors 50, 51
Become conductive, the collector voltages of the transistors 50 and 51 become almost 0V, and these 0V voltages are applied to the attenuator 26, the attenuator 26 does not operate, and the attenuation amount becomes the minimum. Therefore, the video level of the satellite broadcast of the selected channel is hardly attenuated because the terminal 30b becomes L level.

When the terminal 30c becomes L level, the output of the inverter 52c becomes H level and the electronic switch 48c is closed.
As a result, the common terminal of the changeover switch 46c is in contact with the M contact to which 6V is applied, so that 6V is applied to the bases of the transistors 50 and 51 via the closed electronic switch 48c. As a result, the transistor 50 in which the Zener diode 54 is inserted on the base side becomes non-conductive,
The transistor 51 in which the Zener diode is not inserted in the base becomes conductive. As a result, the collector voltage of the transistor 50 becomes 12V, the collector voltage of the transistor 51 becomes almost 0V, and the collector voltage of these 12V becomes almost 0V.
Are supplied to the attenuator 26, and the attenuation amount of the attenuator 26 becomes medium. Therefore, the video level of the satellite broadcast of the selected channel is attenuated to the middle level by the terminal 30a becoming the L level.

Similarly, when the other terminals 30d to 30h become the L level, the attenuation amount of the attenuating unit 26 becomes the attenuation amount corresponding to the applied voltage of the contact with which the common terminal of the changeover switches 46d to 46h is in contact.

In the above embodiment, the common terminals of the changeover switches 46a to 46c are in contact with the H contact, the L contact, and the M contact, respectively. However, the present invention is not limited to this, and the satellite broadcast of the channel to be received. Any contact may be contacted depending on the video level of.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a satellite broadcast receiving converter in which a channel selecting device according to the present invention is implemented.
FIG. 2 is a detailed circuit diagram of the frequency adjustment unit and attenuation control unit of the same embodiment, and FIG. 3 is a block diagram of a satellite broadcast receiving tuner using a conventional channel selection device. 2 ... High frequency / frequency converter, 6 ... Frequency adjuster, 10
...... Channel selection section, 26 …… Attenuation section.

Claims (1)

(57) [Scope of utility model registration request] 1. A channel selection unit for generating a selection signal for selecting any one of a plurality of channels of FM-modulated video signals, and a frequency conversion unit for converting the FM-modulated video signals of the selected channels into intermediate frequencies. A frequency adjustment unit that supplies a frequency adjustment signal to the frequency conversion unit according to the selection signal so as to be converted into a signal, a detection unit that FM-detects the intermediate frequency signal from the frequency conversion unit, and from this detection unit. The attenuation control section is provided in a subsequent stage and changes the amount of attenuation according to the magnitude of the attenuation control signal, and the attenuation control section supplies the attenuation control signal to the attenuation section. It is configured to generate a plurality of attenuation control signals preset so as to generate an attenuation amount suitable for each channel corresponding to each selection signal in the attenuation unit, and when the selection signal is input. Channel selection apparatus characterized by generating said attenuation control signal corresponding thereto.